Sulfonate-functional coatings and methods

ABSTRACT

A coating composition is described comprising: (i) a zwitterionic compound comprising sulfonate-functional groups and alkoxysilane groups and/or silanol-functional groups; (ii) alcohol and/or water; and (iii) a tetraalkoxysilane, oligomers thereof, lithium silicate, sodium silicate, potassium silicate, silica, or combinations thereof, along with coated articles and methods of using.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.13/511,714, filed May 24, 2012 and issued as U.S. Pat. No. 9,340,683 onMay 17, 2016, which is a national stage filing under 35 U.S.C. 371 ofPCT/US2010/060915, filed Dec. 17, 2010, which claims priority to U.S.Provisional Application No. 61/287,555, filed Dec. 17, 2009, thedisclosure of which is incorporated by reference in its/their entiretyherein.

BACKGROUND

Articles having surfaces capable of being easily cleaned of fingerprintsare highly desirable for a variety of uses, particularly surfaces ofcomputer screens, cell phones, and the like. Currently available coatingcompositions used on such products do not provide a surface from whichfingerprints can be easily removed.

SUMMARY

The present disclosure is directed to a coated article having asubstrate surface coated with a sulfonate-functional coating.Preferably, such coating includes at least a monolayer of asulfonate-functional compound. The present disclosure also providesmethods, including methods of making a coated substrate (i.e., treatinga substrate surface) and methods of removing fingerprints from thecoated substrate.

Significantly, for substrates having a sulfonate-functional coatingthereon as described herein, a simple application of gentle wiping isall that is needed to remove substantially all of the skin oilsdeposited as a fingerprint; however, for preferred embodiments water(e.g., tap water at ambient temperature) and/or water vapor (e.g., anindividual's breath) and wiping (e.g., up to a few gentle strokes with atissue, paper towel, cloth) is all that is necessary to removesubstantially all of the skin oils deposited as a fingerprint.

In one embodiment, there is provided a method of treating a substratesurface. The method includes: applying a primer coating composition tothe substrate surface to form a primed surface having —OH groupsthereon; contacting the primed surface having —OH groups thereon with asulfonate-functional coating composition, wherein thesulfonate-functional coating composition includes a zwitterioniccompound having sulfonate-functional groups and alkoxysilane groupsand/or silanol-functional groups. The method further includes drying thesulfonate-functional coating composition to form a sulfonate-functionalcoating including at least a monolayer of the sulfonate-functionalcompound bonded to the primer coating through siloxane bonds; whereinfingerprints are removable from the dried sulfonate-functional coatingwith water and/or water vapor, and wiping.

In one embodiment, there is provided a method of treating a substratesurface. The method includes: applying a primer coating composition tothe substrate surface to form a primed surface comprising nanoparticles;contacting the primed surface with a sulfonate-functional coatingcomposition, wherein the sulfonate-functional coating compositionincludes a non-zwitterionic compound having sulfonate-functional groupsand alkoxysilane groups and/or silanol-functional groups. The methodfurther includes drying the sulfonate-functional coating composition toform a sulfonate-functional coating including at least a monolayer ofthe sulfonate-functional compound bonded to the primer coating throughsiloxane bonds; wherein fingerprints are removable from the driedsulfonate-functional coating with water and/or water vapor, and wiping.

In certain embodiments, applying a primer coating composition to thesubstrate surface involves contacting the substrate surface with ananoparticle-containing coating composition. The nanoparticle-containingcoating composition includes an aqueous dispersion having a pH of lessthan 5 including silica nanoparticles having average particle diametersof 40 nanometers or less, and an acid having a pKa of ≤3.5. The methodfurther includes drying the nanoparticle-containing coating compositionto provide a silica nanoparticle primer coating on the substratesurface. In certain embodiments, if desired, the nanoparticle-containingcoating composition further includes a tetraalkoxysilane.

In another embodiment, the present disclosure provides a method oftreating a substrate that includes a metal or organic polymeric surfaceto improve fingerprint removal. The method includes: contacting themetal or organic polymeric surface with a sulfonate-functional coatingcomposition, wherein the sulfonate-functional coating compositionincludes a zwitterionic compound having sulfonate-functional groups andalkoxysilane groups and/or silanol-functional groups; and drying thesulfonate-functional coating composition to form a sulfonate-functionalcoating. The sulfonate-functional coating includes at least a monolayerof the sulfonate-functional compound bonded to the substrate surfacethrough siloxane bonds.

In another embodiment, the present disclosure provides a method oftreating a substrate that includes a metal or organic polymeric surfaceto improve fingerprint removal. The method includes: contacting themetal or organic polymeric surface with a sulfonate-functional coatingcomposition, wherein the sulfonate-functional coating compositionincludes a non-zwitterionic compound having sulfonate-functional groupsand alkoxysilane groups and/or silanol-functional groups; and drying thesulfonate-functional coating composition to form a sulfonate-functionalcoating. The sulfonate-functional coating includes at least a monolayerof the sulfonate-functional compound bonded to the substrate surfacethrough siloxane bonds.

Advantageously, fingerprints are removable from the driedsulfonate-functional coating with wiping, and preferably with waterand/or water vapor and wiping. For example, fingerprints are easilyremoved from the sulfonate-functional surfaces by simply gently wipingwhen the surfaces are saturated with water/moisture by breathing.

The present disclosure also provides a hydrophilic article prepared froma method of the disclosure.

In particular, in one embodiment, there is provided a coated articlethat includes a substrate surface, a primer coating disposed on thesubstrate surface, and a sulfonate-functional zwitterionic coatingbonded to the primer coating through siloxane bonds.

In another embodiment, there is provided a coated article that includesa substrate surface, a nanoparticle-containing primer disposed on thesubstrate surface, and a sulfonate-functional zwitterionic coatingbonded to the nanoparticle-containing primer through siloxane bonds. Thenanoparticle-containing primer includes agglomerates of silicananoparticles having average particle diameters of 40 nanometers orless, said agglomerates including a three-dimensional porous network ofsilica nanoparticles, and the silica nanoparticles are bonded toadjacent silica nanoparticles.

In another embodiment, there is provided a coated article that includesa substrate surface, a nanoparticle-containing primer disposed on thesubstrate surface, and a sulfonate-functional coating bonded to thenanoparticle-containing primer through siloxane bonds. Thenanoparticle-containing primer includes agglomerates of a silicananoparticles having average particle diameters of 40 nanometers or lessand silica nanoparticles having average particle diameters of greaterthan 50 nanometers, said agglomerates comprising a three-dimensionalporous network of silica nanoparticles, and the silica nanoparticles arebonded to adjacent silica nanoparticles.

In another embodiment, there is provided a coated article that includesa substrate surface, a nanoparticle-containing primer disposed on thesubstrate surface, and a sulfonate-functional non-zwitterionic coatingbonded to the nanoparticle-containing primer through siloxane bonds. Thenanoparticle-containing primer includes agglomerates of silicananoparticles having average particle diameters of 40 nanometers orless, said agglomerates including a three-dimensional porous network ofsilica nanoparticles, and the silica nanoparticles are bonded toadjacent silica nanoparticles.

In certain embodiments of the coated article, the substrate surfaceincludes a metal surface, a ceramic surface, an organic polymericsurface, or a combination thereof. In certain embodiments of the coatedarticle, the substrate surface includes a metal surface, an organicpolymeric surface, or a combination thereof. In certain embodiments ofthe coated article, the sulfonate-functional coating includes at least amonolayer of a sulfonate-functional compound bonded to thenanoparticle-containing primer through siloxane bonds.

In certain embodiments of the coated article, thenanoparticle-containing primer coating is 100 angstroms (Å) to 10,000 Åthick. In certain embodiments of the coated article, thesulfonate-functional coating is no greater than 10 microns thick, andoften no greater than 1 micron thick.

The present disclosure also provides methods of removing fingerprintsfrom a surface.

In one embodiment of removing fingerprints from a surface, the methodincludes: receiving a coated article including a substrate surface and asulfonate-functional zwitterionic coating bonded to the substratesurface through siloxane bonds; and removing fingerprints from thesulfonate-functional surface by wiping the fingerprints.

In one embodiment of removing fingerprints from a surface, the methodincludes: receiving a coated article including a substrate surface thatincludes a primer (preferably a nanoparticle-containing primer) disposedon the substrate surface, and a sulfonate-functional zwitterioniccoating bonded to the nanoparticle-containing primer through siloxanebonds; and removing fingerprints from the sulfonate-functional surfaceby wiping the fingerprints.

Surprisingly, it has been found that sulfonate-functional zwitterioniccompounds provide much easier fingerprint removal than similarcarboxylate-functional zwitterionic compounds when the positive chargeof the zwitterions is derived from a quaternary ammonium moiety.

In one embodiment of removing fingerprints from a surface, the methodincludes: receiving a coated article including a substrate surface thatincludes a nanoparticle-containing primer disposed on the substratesurface, and a sulfonate-functional non-zwitterionic coating bonded tothe nanoparticle-containing primer through siloxane bonds; and removingfingerprints from the sulfonate-functional surface by wiping thefingerprints.

In some embodiments, the methods of removing fingerprints from thesulfonate-functional surface include applying water and/or water vaporto the fingerprints and wiping.

In another embodiment, the present disclosure provides a coatingcomposition that includes: a zwitterionic compound includingsulfonate-functional groups and alkoxysilane groups and/orsilanol-functional groups; alcohol and/or water; and atetraalkoxysilane, oligomers thereof, lithium silicate, sodium silicate,potassium silicate, silica, or combinations thereof.

In another embodiment, the present disclosure provides a coatingcomposition that includes: a non-zwitterionic compound includingsulfonate-functional groups and alkoxysilane groups and/orsilanol-functional groups; alcohol and/or water; and atetraalkoxysilane, oligomers thereof, lithium silicate, sodium silicate,potassium silicate, silica, or combinations thereof.

Definitions

The terms “comprises” and variations thereof do not have a limitingmeaning where these terms appear in the description and claims.

The words “preferred” and “preferably” refer to embodiments of thedisclosure that may afford certain benefits, under certaincircumstances. However, other embodiments may also be preferred, underthe same or other circumstances. Furthermore, the recitation of one ormore preferred embodiments does not imply that other embodiments are notuseful, and is not intended to exclude other embodiments from the scopeof the invention.

As used herein, “a,” “an,” “the,” “at least one,” and “one or more” areused interchangeably.

As used herein, the term “or” is generally employed in its senseincluding “and/or” unless the content clearly dictates otherwise. Theterm “and/or” means one or all of the listed elements or a combinationof any two or more of the listed elements.

As used herein, all numbers are assumed to be modified by the term“about” and preferably by the term “exactly.” Notwithstanding that thenumerical ranges and parameters setting forth the broad scope of theinvention are approximations, the numerical values set forth in thespecific examples are reported as precisely as possible. All numericalvalues, however, inherently contain certain errors necessarily resultingfrom the standard deviation found in their respective testingmeasurements.

Also herein, the recitations of numerical ranges by endpoints includeall numbers subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2,2.75, 3, 3.80, 4, 5, etc.).

The term “in the range” or “within a range” (and similar statements)includes the endpoints of the stated range.

Groupings of alternative elements or embodiments disclosed herein arenot to be construed as limitations. Each group member may be referred toand claimed individually or in any combination with other members of thegroup or other elements found therein. It is anticipated that one ormore members of a group may be included in, or deleted from, a group forreasons of convenience and/or patentability. When any such inclusion ordeletion occurs, the specification is herein deemed to contain the groupas modified thus fulfilling the written description of all Markushgroups used in the appended claims.

When a group is present more than once in a formula described herein,each group is “independently” selected, whether specifically stated ornot. For example, when more than one Y group is present in a formula,each Y group is independently selected. Furthermore, subgroups containedwithin these groups are also independently selected. For example, wheneach Y group contains an R, then each R is also independently selected.

As used herein, the term “organic group” means a hydrocarbon group (withoptional elements other than carbon and hydrogen, such as oxygen,nitrogen, sulfur, and silicon) that is classified as an aliphatic group,cyclic group, or combination of aliphatic and cyclic groups (e.g.,alkaryl and aralkyl groups). In the context of the present disclosure,the organic groups are those that do not interfere with the formation ofa wipe-away fingerprint surface. The term “aliphatic group” means asaturated or unsaturated linear or branched hydrocarbon group. This termis used to encompass alkyl, alkenyl, and alkynyl groups, for example.The term “alkyl group” means a saturated linear or branched hydrocarbongroup including, for example, methyl, ethyl, isopropyl, t-butyl, heptyl,dodecyl, octadecyl, amyl, 2-ethylhexyl, and the like. The term “alkylenegroup” is a divalent alkyl group. The term “alkenyl group” means anunsaturated, linear or branched hydrocarbon group with one or morecarbon-carbon double bonds, such as a vinyl group. The term “alkynylgroup” means an unsaturated, linear or branched hydrocarbon group withone or more carbon-carbon triple bonds. The term “cyclic group” means aclosed ring hydrocarbon group that is classified as an alicyclic group,aromatic group, or heterocyclic group. The term “alicyclic group” meansa cyclic hydrocarbon group having properties resembling those ofaliphatic groups. The term “aromatic group” or “aryl group” means amono- or polynuclear aromatic hydrocarbon group. The term “heterocyclicgroup” means a closed ring hydrocarbon in which one or more of the atomsin the ring is an element other than carbon (e.g., nitrogen, oxygen,sulfur, etc.). A group that may be the same or different is referred toas being “independently” something.

Substitution is anticipated on the organic groups of the complexes ofthe present disclosure. As a means of simplifying the discussion andrecitation of certain terminology used throughout this application, theterms “group” and “moiety” are used to differentiate between chemicalspecies that allow for substitution or that may be substituted and thosethat do not allow or may not be so substituted. Thus, when the term“group” is used to describe a chemical substituent, the describedchemical material includes the unsubstituted group and that group withO, N, Si, or S atoms, for example, in the chain (as in an alkoxy group)as well as carbonyl groups or other conventional substitution. Where theterm “moiety” is used to describe a chemical compound or substituent,only an unsubstituted chemical material is intended to be included. Forexample, the phrase “alkyl group” is intended to include not only pureopen chain saturated hydrocarbon alkyl substituents, such as methyl,ethyl, propyl, t-butyl, and the like, but also alkyl substituentsbearing further substituents known in the art, such as hydroxy, alkoxy,alkylsulfonyl, halogen atoms, cyano, nitro, amino, carboxyl, etc. Thus,“alkyl group” includes ether groups, haloalkyls, nitroalkyls,carboxyalkyls, hydroxyalkyls, sulfoalkyls, etc. On the other hand, thephrase “alkyl moiety” is limited to the inclusion of only pure openchain saturated hydrocarbon alkyl substituents, such as methyl, ethyl,propyl, t-butyl, and the like.

The term “primary particle size” refers to the average size ofunagglomerated single particles of silica.

As used herein, “hydrophilic” is used to refer to a surface that is wetby aqueous solutions, and does not express whether or not the layerabsorbs aqueous solutions. Surfaces on which drops of water or aqueoussolutions exhibit a static water contact angle of less than 50° arereferred to as “hydrophilic”. Hydrophobic substrates have a watercontact angle of 50° or greater.

As used herein, “at least a monolayer of a sulfonate-functionalcompound” includes a monolayer or a thicker layer of molecules,covalently bonded (through siloxane bonds) to the surface or primer onthe surface of a substrate, wherein such molecules are derived from thesulfonate-functional compound. If the sulfonate-functional compoundincludes dimers, trimers, or other oligomers of individual molecules,then “at least a monolayer” would include a monolayer of such dimers,trimers, or other oligomers, or a mixture of such oligomers withmonomers.

The above summary of the present disclosure is not intended to describeeach disclosed embodiment or every implementation of the presentinvention. The description that follows more particularly exemplifiesillustrative embodiments. In several places throughout the application,guidance is provided through lists of examples, which examples can beused in various combinations. In each instance, the recited list servesonly as a representative group and should not be interpreted as anexclusive list.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a substrate having a surface on which is coated a primerand a sulfonate-functional coating thereon, according to one embodimentof the invention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The present disclosure is directed to a coated article having asubstrate surface coated with a layer of a sulfonate-functional coating.Preferably, such coating includes at least a monolayer of asulfonate-functional compound.

Significantly, fingerprints can be easily removed from thesulfonate-functional coating of the present disclosure with wiping,preferably after first applying water and/or water vapor (e.g., bybreathing) to the fingerprints. Typically, methods of the presentdisclosure include removing fingerprints (by this it is meant,substantially all the skin oils deposited as a fingerprint) from thesulfonate-functional surface by simply applying water (e.g., tap waterat room temperature) and/or water vapor (e.g., a person's breath) andwiping. Herein, “wiping” refers to gentle wiping, typically by hand,with for example, a tissue, paper towel, or a cloth, without significantpressure (e.g., generally, no more than 350 grams) for one or morestrokes or rubs (typically, only a few are needed).

In particular, in one embodiment, there is provided a coated articlethat includes a substrate surface, a primer (preferably, ananoparticle-containing primer) disposed on the substrate surface, and asulfonate-functional coating disposed on the primed surface. See, forexample, FIG. 1.

FIG. 1 which shows a substrate 10 having a surface 12 on which is coateda primer coating 14 and a sulfonate-functional coating 16 thereon,according to one embodiment of the invention. The sulfonate-functionalcoating is preferably applied in a monolayer thickness, but can be asthick as 10 microns. The primer coating is preferably within a range of100 angstroms (Å) to 10,000 Å thick, and frequently 500 Å to 2500 Åthick.

Siloxane (Si—O—Si) bonds are used to chemically bind the sulfonatefunctionality to the surface, whether it be directly to the substratesurface or to a primer coating thereon. Preferably, the presence ofthree siloxane bonds for each surface sulfonate group makes the chemicalbond relatively more stable than if one or two siloxane bonds wereformed.

In one particular embodiment, a coated article includes a substratesurface, a nanoparticle-containing primer disposed on the substratesurface, and a sulfonate-functional coating bonded to thenanoparticle-containing primer through siloxane bonds. Thenanoparticle-containing primer includes agglomerates of silicananoparticles having average particle diameters of 40 nanometers orless, said agglomerates including a three-dimensional porous network ofsilica nanoparticles, and the silica nanoparticles are bonded toadjacent silica nanoparticles.

In one embodiment, there is provided a method of treating a substratesurface. The method includes: applying a primer coating composition tothe substrate surface to form a primed surface having —OH groupsthereon; contacting the primed surface having —OH groups thereon with asulfonate-functional coating composition, wherein thesulfonate-functional coating composition includes an organic compoundhaving sulfonate-functional groups and alkoxysilane groups and/orsilanol-functional groups. The method further includes drying thesulfonate-functional coating composition to form a sulfonate-functionalcoating including at least a monolayer of the sulfonate-functionalcompound bonded to the primer coating through siloxane bonds; whereinfingerprints are removable from the dried sulfonate-functional coatingby wiping, or preferably by applying water and/or water vapor (e.g., bybreathing) with wiping. In certain embodiments, the sulfonate-functionalorganic compound is a zwitterionic compound and in certain embodiments,it is a non-zwitterionic compound.

The sulfonate-functional coating compositions of the present disclosurecan be used on a variety of substrate surfaces, including for example, ametal surface, an organic polymeric surface, or a combination thereof.The method includes: contacting the metal or organic polymeric surfacewith a sulfonate-functional coating composition, wherein thesulfonate-functional coating composition includes an organic compoundhaving sulfonate-functional groups and alkoxysilane groups and/orsilanol-functional groups; and drying the sulfonate-functional coatingcomposition to form a sulfonate-functional coating. Thesulfonate-functional coating includes at least a monolayer of thesulfonate-functional compound bonded to the substrate surface throughsiloxane bonds. In certain embodiments, the sulfonate-functional organiccompound is a zwitterionic compound and in certain embodiments, it is anon-zwitterionic compound.

Advantageously, fingerprints are removable from the driedsulfonate-functional coating with wiping, and preferably with waterand/or water vapor and wiping. For example, fingerprints are easilyremoved from the sulfonate-functional surfaces by simply gently wipingwhen the surfaces are saturated with water/moisture by breathing.

Thus, the methods of the present disclosure can be used to prepare ahydrophilic article on a surface of a wide variety of substrates,thereby providing “wipe-away fingerprint surfaces.” Such surface is onehaving a sulfonate-functional coating thereon that can be cleaned ofsubstantially all the skin oils deposited as a fingerprint by a simpleapplication of gentle wiping with a cloth, paper towel, tissue, or thelike. Preferably, such “wipe-away fingerprint surfaces” are those thatcan be cleaned of substantially all the skin oils deposited as afingerprint by wiping, or preferably by applying water (e.g., tap waterat ambient temperature) and/or water vapor (e.g., an individual'sbreath) and wiping (e.g., up to a few gentle strokes with a tissue,paper towel, cloth).

In certain embodiments of the coated article, the sulfonate-functionalcoating includes at least a monolayer of a sulfonate-functional compoundbonded to the substrate surface through siloxane bonds. In certainembodiments of the coated article, the sulfonate-functional coatingincludes at least a monolayer of a sulfonate-functional compound bondedto a primer through siloxane bonds. In certain embodiments of the coatedarticle, the sulfonate-functional coating includes at least a monolayerof a sulfonate-functional compound bonded to a nanoparticle-containingprimer through siloxane bonds. The present disclosure also provides ahydrophilic article prepared from a method of the disclosure.

The present disclosure also provides methods of removing fingerprintsfrom a surface.

Generally, such methods include: receiving a coated article including asubstrate surface that optionally includes a primer (e.g., ananoparticle-containing primer) disposed on the substrate surface, and asulfonate-functional coating bonded to the substrate surface or theprimer through siloxane bonds; and removing fingerprints from thesulfonate-functional surface by wiping the fingerprints. Preferably, themethods of removing fingerprints from the sulfonate-functional surfaceinclude applying water and/or water vapor to the fingerprints andwiping.

In another embodiment, the present disclosure provides a coatingcomposition that includes: an organic compound (in certain embodiments,a zwitterionic compound, and in certain embodiments, a non-zwitterioniccompound) including sulfonate-functional groups and alkoxysilane groupsand/or silanol-functional groups; alcohol and/or water; and atetraalkoxysilane, oligomers of tetraalkoxysilanes, lithium silicate,sodium silicate, potassium silicate, silica (e.g., silica particles suchas silica nanoparticles), or combinations thereof.

Sulfonate-Functional Coating

The sulfonate-functional coating can be prepared fromsulfonate-functional compounds. These compounds have an alkoxysilane-and/or silanol-functional group for bonding to a substrate surface. Theyalso include a sulfonate group (SO₃ ⁻) for rendering hydrophilicity tothe substrate surface.

For certain embodiments, the sulfonate-containing compounds arezwitterionic and for certain embodiments, they are non-zwitterionic.

Examples include non-zwitterionic sulfonate-organosilanol compounds suchas those disclosed in U.S. Pat. No. 4,152,165 (Langager et al.) and U.S.Pat. No. 4,338,377 (Beck et al.).

In certain embodiments, the non-zwitterionic sulfonate-organosilanolcompounds used in the solutions and compositions of the presentdisclosure have the following Formula (I):[(MO)(Q_(n))Si(XCH₂SO₃ ⁻)_(3-n)]Y_(2/nr) ^(+r)  (I)wherein:

each Q is independently selected from hydroxyl, alkyl groups containingfrom 1 to 4 carbon atoms and alkoxy groups containing from 1 to 4 carbonatoms;

M is selected from hydrogen, alkali metals, and organic cations ofstrong organic bases having an average molecular weight of less than 150and a pKa of greater than 11;

X is an organic linking group;

Y is selected from hydrogen, alkaline earth metals (e.g., magnesium,calcium, etc.), organic cations of protonated weak bases having anaverage molecular weight of less than 200 and a pKa of less than 11(e.g., 4-aminopyridine, 2-methoxyethylamine, benzylamine,2,4-dimethylimidazole, 3-[2-ethoxy(2-ethoxyethoxy)]propylamine), alkalimetals, and organic cations of strong organic bases having an averagemolecular weight of less than 150 and a pKa of greater than 11 (e.g.,⁺N(CH₃)₄, ⁺N(CH₂CH₃)₄), provided that M is hydrogen when Y is selectedfrom hydrogen, alkaline earth metals and organic cations of saidprotonated weak bases;

r is equal to the valence of Y; and

n is 1 or 2.

Preferably, the non-zwitterionic compound of Formula (I) is analkoxysilane compound (e.g., wherein Q is an alkoxy group containingfrom 1 to 4 carbon atoms).

The weight percentage of oxygen in these compounds of Formula (I) is atleast 30%, and preferably at least 40%. Most preferably it is in therange of 45% to 55%. The weight percentage of silicon in these compoundsis no greater than 15%. Each of these percentages is based on the weightof the compound in the water-free acid form.

The organic linking group X of Formula (I) is preferably selected fromalkylene groups, cycloalkylene groups, alkyl-substituted cycloalkylenegroups, hydroxy-substituted alkylene groups, hydroxy-substitutedmono-oxa alkylene groups, divalent hydrocarbon groups having mono-oxabackbone substitution, divalent hydrocarbon groups having mono-thiabackbone substitution, divalent hydrocarbon groups having monooxo-thiabackbone substitution, divalent hydrocarbon groups having dioxo-thiabackbone substitution, arylene groups, arylalkylene groups, alkylarylenegroups and substituted alkylarylene groups. Most preferably X isselected from alkylene groups, hydroxy-substituted alkylene groups andhydroxy-substituted mono-oxa alkylene groups.

Suitable examples of non-zwitterionic compounds of Formula (I) aredescribed in U.S. Pat. No. 4,152,165 (Langager et al.) and U.S. Pat. No.4,338,377 (Beck et al.), and include, for example, the following:(HO)₃Si—CH₂CH₂CH₂—O—CH₂—CH(OH)—CH₂SO₃ ⁻H⁺;(HO)₃Si—CH₂CH(OH)—CH₂SO₃ ⁻H⁺;(HO)₃Si—CH₂CH₂CH₂SO₃ ⁻H⁺;(HO)₃Si—C₆H₄—CH₂CH₂SO₃ ⁻H⁺;(HO)₂Si—[CH₂CH₂SO₃ ⁻H⁺]₂;(HO)—Si(CH₃)₂—CH₂CH₂SO₃ ⁻H⁺;(NaO)(HO)₂Si—CH₂CH₂CH₂—O—CH₂—CH(OH)—CH₂SO₃ ⁻Na⁺;and(HO)₃Si—CH₂CH₂SO₃ ⁻K⁺.

Examples of zwitterionic sulfonate-functional compounds include thosedisclosed in U.S. Pat. No. 5,936,703 (Miyazaki et al.) and InternationalPublication Nos. WO 2007/146680 and WO 2009/119690.

In certain embodiments, the zwitterionic sulfonate-organosilanolcompounds used in the solutions and compositions of the presentdisclosure have the following Formula (II) wherein:(R¹O)_(p)—Si(R²)_(q)—W—N⁺(R³)(R⁴)—(CH₂)_(m)—SO₃ ⁻  (II)wherein:

each R¹ is independently a hydrogen, methyl group, or ethyl group;

each R² is independently a methyl group or an ethyl group;

each R³ and R⁴ is independently a saturated or unsaturated, straightchain, branched, or cyclic organic group, which may be joined together,optionally with atoms of the group W, to form a ring;

W is an organic linking group;

p and m are integers of 1 to 3;

q is 0 or 1; and

p+q=3.

The organic linking group W of Formula (II) is preferably selected fromsaturated or unsaturated, straight chain, branched, or cyclic organicgroups. The linking group W is preferably an alkylene group, which mayinclude carbonyl groups, urethane groups, urea groups, heteroatoms suchas oxygen, nitrogen, and sulfur, and combinations thereof. Examples ofsuitable linking groups W include alkylene groups, cycloalkylene groups,alkyl-substituted cycloalkylene groups, hydroxy-substituted alkylenegroups, hydroxy-substituted mono-oxa alkylene groups, divalenthydrocarbon groups having mono-oxa backbone substitution, divalenthydrocarbon groups having mono-thia backbone substitution, divalenthydrocarbon groups having monooxo-thia backbone substitution, divalenthydrocarbon groups having dioxo-thia backbone substitution, arylenegroups, arylalkylene groups, alkylarylene groups and substitutedalkylarylene groups.

Suitable examples of zwitterionic compounds of Formula (II) aredescribed in U.S. Pat. No. 5,936,703 (Miyazaki et al.) and InternationalPublication Nos. WO 2007/146680 and WO 2009/119690, and include thefollowing zwitterionic functional groups (—W—N⁺(R³)(R⁴)—(CH₂)_(m)—SO₃⁻):

In certain embodiments, the sulfonate-organosilanol compounds used inthe solutions and compositions of the present disclosure have thefollowing Formula (III) wherein:(R¹O)_(p)—Si(R²)_(q)—CH₂CH₂CH₂—N⁺(CH₃)₂—(CH₂)_(m)—SO₃ ⁻  (III)wherein:

each R¹ is independently a hydrogen, methyl group, or ethyl group;

each R² is independently a methyl group or an ethyl group;

p and m are integers of 1 to 3;

q is 0 or 1; and

p+q=3.

Suitable examples of zwitterionic compounds of Formula (III) aredescribed in U.S. Pat. No. 5,936,703 (Miyazaki et al.), including, forexample:(CH₃O)₃Si—CH₂CH₂CH₂—N⁺(CH₃)₂—CH₂CH₂CH₂—SO₃ ⁻;and(CH₃CH₂O)₂Si(CH₃)—CH₂CH₂CH₂—N⁺(CH₃)₂—CH₂CH₂CH₂—SO₃ ⁻.

Other examples of suitable zwitterionic compounds, which can be madeusing standard techniques that are exemplified in the Examples Section,include the following:

Preferred examples of suitable sulfonate-functional compounds for use inpreparing coating compositions and coatings of the present disclosureare described in the Experimental Section.

The sulfonate-functional coating composition typically includes asulfonate-functional compound in an amount of at least 0.1 wt-%, andoften at least 1 wt-%, based on the total weight of the coatingcomposition. The sulfonate-functional coating composition typicallyincludes a sulfonate-functional compound in an amount of no greater than20 wt-%, and often no greater than 5 wt-%, based on the total weight ofthe coating composition. Generally, for monolayer coating thicknesses,relatively dilute coating compositions are used. Alternatively,relatively concentrated coating compositions can be used andsubsequently rinsed.

The sulfonate-functional coating composition preferably includesalcohol, water, or hydroalcoholic solutions (i.e., alcohol and/orwater). Typically, such alcohols are lower alcohols (e.g., C₁ to C₈alcohols, and more typically C₁ to C₄ alcohols), such as methanol,ethanol, propanol, 2-propanol, etc. Preferably, the sulfonate-functionalcoating compositions are aqueous solutions. As it is used herein, theterm “aqueous solution” refers to solutions containing water. Suchsolutions may employ water as the only solvent or they may employcombinations of water and organic solvents such as alcohol and acetone.Organic solvents may also be included in the hydrophilic treatmentcompositions so as to improve their freeze-thaw stability. Typically,the solvents are present in an amount up to 50% by weight of thecompositions and preferably in the range of 5-50% by weight of thecompositions.

The sulfonate-functional coating composition can be acidic, basic, orneutral. The performance durability of the coatings can be affected bypH. For example, coating compositions containing sulfonate-functionalzwitterionic compounds are preferably neutral.

The sulfonate-functional coating compositions may be provided in avariety of viscosities. Thus, for example, the viscosity may vary from awater-like thinness to a paste-like heaviness. They may also be providedin the form of gels. Additionally, a variety of other ingredients may beincorporated in the compositions.

Thus, for example, conventional surfactants, cationic, anionic, ornonionic surfactants can be used. Detergents and wetting agents can alsobe used. Typically, anionic surfactants, detergents, and wetting agentssuch as those described below for the Primer Composition are also usefulin the sulfonate-functional coating compositions of the disclosure.

In certain embodiments, the sulfonate-functional coating compositionfurther includes a tetraalkoxysilane (e.g., tetraethylorthosilicate(TEOS)), oligomers thereof, such as alkyl polysilicates (e.g.,poly(diethoxysiloxane)), lithium silicate, sodium silicate, potassiumsilicate, silica (e.g., silica particles), or combinations thereof,which can provide enhanced durability. In some embodiments, the amountof such coupling agent included in the coating composition should belimited in order to prevent destruction of the anti-reflective oranti-fog properties of the coating. The optimal amount of coupling agentis determined experimentally and is dependent on the coupling agent'sidentity, molecular weight and refractive index. The coupling agent(s),when present, are typically added to the composition at levels of 0.1 to20 percent by weight of the coating composition, and more preferably 1to 15 percent by weight of the coating composition.

Sulfonate-functional coating compositions are preferably coated on thearticle using conventional techniques, such as bar, roll, curtain,rotogravure, spray, or dip coating techniques. The preferred methodsinclude bar and roll coating, or air knife coating to adjust thickness.

The sulfonate-functional coatings of the present disclosure arepreferably applied in a monolayer thickness. Typically, thesulfonate-functional coating is no greater than 10 microns thick, andpreferably no greater than 1 micron thick, as measured using anellipsometer such as a Gaertner Scientific Corp Model No. L115C.

Sulfonate-functional coatings of the present disclosure can be coated onboth sides of a substrate if desired. Alternatively, the coatings of thepresent disclosure may be coated on one side of the substrate. Oncecoated, the sulfonate-functional article is typically dried attemperatures of 20° C. to 150° C. in a recirculating oven. An inert gasmay be circulated. The temperature may be increased further to speed thedrying process, but care must be exercised to avoid damage to thesubstrate.

The sulfonate-functional coating compositions provide anti-fogproperties to surfaces coated therewith. The anti-fog property isdemonstrated by the tendency of the coatings to resist the formation ofwater droplets which tend to significantly reduce the transparency ofthe coated substrate. Water vapor from, for example, human breathing,tends to condense upon the coated substrate in the form of a thinuniform water film, rather than as water droplets. Such a uniform filmdoes not significantly reduce the clarity or transparency of thesubstrate.

Primer Coating

In certain embodiments of the present disclosure, a primer coating isformed on a substrate surface. Such primer coating provides —OH groupson the substrate surface. Preferably, such primer coating is formed froma nanoparticle-containing coating composition that is coated and driedon a substrate surface.

Other primer compositions or processes can be used to provide —OHgroups. Examples of such compositions include a tetraalkoxysilane,oligomers thereof, lithium silicate, sodium silicate, potassiumsilicate, silica (e.g., silica particles), or combinations thereof. Incertain embodiments, the described surface in this disclosure can besurface modified by the conventional vapor coating or vapor depositionprocess to create SiO or SiO₂ thin layer primers described in U.S. Pat.No. 4,338,377. Surface modification of substrates may also include vaporcoating or vapor deposition of alkoxysilanes. Although the followingdiscussion focuses on nanoparticle-containing primer coatings, variousfeatures described (e.g., coating thickness) apply to other primercoatings.

In certain embodiments, the nanoparticle-containing primer coatingcomposition includes an aqueous dispersion having a pH of less than 5comprising silica nanoparticles having average particle diameters of 40nanometers or less, and an acid having a pKa of ≤3.5 (preferably <2.5,most preferably less than 1).

In another embodiment, the nanoparticle-containing primer coatingcomposition comprises silica nanoparticles having a bi-modaldistribution.

These acidified silica nanoparticle primer coating compositions, can becoated directly onto hydrophobic organic and inorganic substrateswithout either organic solvents or surfactants. The wetting property ofthese inorganic nanoparticle aqueous dispersions on hydrophobic surfacessuch as polyethylene terephthalate (PET) or polycarbonate (PC) is afunction of the pH of the dispersions and the pKa of the acid. Theprimer coating compositions are coatable on hydrophobic organicsubstrates when they are acidified with HCl to pH=2 to 3, and even to 5in some embodiments. In contrast, the primer coating compositions beadup on the organic substrates at neutral or basic pH.

Inorganic silica sols in aqueous media are well known in the art andavailable commercially. Silica sols in water or water-alcohol solutionsare available commercially under such trade names as LUDOX (manufacturedby E.I. duPont de Nemours and Co., Inc., Wilmington, Del.), NYACOL(available from Nyacol Co., Ashland, Mass.) or NALCO (manufactured byOndea Nalco Chemical Co., Oak Brook, Ill.). One useful silica sol isNALCO 2326 available as a silica sol with mean particle size of 5nanometers, pH 10.5, and solid content 15% by weight. Other commerciallyavailable silica nanoparticles include “NALCO 1115” and “NALCO 1130,”commercially available from NALCO Chemical Co., “Remasol SP30,”commercially available from Remet Corp., and “LUDOX SM,” commerciallyavailable from E.I. Du Pont de Nemours Co., Inc., and Snowtex ST-OUP,Snowtex ST-UP, Snowtex ST-PS-S available from Nissan Chemical Co.

Non-aqueous silica sols (also called silica organosols) may also be usedand are silica sol dispersions wherein the liquid phase is an organicsolvent, or an aqueous organic solvent. In the practice of thisdisclosure, the silica sol is chosen so that its liquid phase istypically aqueous or an aqueous organic solvent. However, it has beenobserved that sodium stabilized silica nanoparticles should first beacidified prior to dilution with an organic solvent such as ethanol.Dilution prior to acidification may yield poor or non-uniform coatings.Ammonium stabilized silica nanoparticles may generally be diluted andacidified in any order.

The primer coating composition contains an acid or combination of acids,each having a pKa (H₂O) of ≤3.5, preferably <2.5, most preferably lessthan 1. Useful acids include both organic and inorganic acids and may beexemplified by oxalic acid, citric acid, H₂SO₃, H₃PO₄, CF₃CO₂H, HCl,HBr, HI, HBrO₃, HNO₃, HC₁O₄, H₂SO₄, CH₃SO₃H, CF₃SO₃H, CF₃CO₂H, andCH₃SO₂OH. Most preferred acids include HCl, HNO₃, H₂SO₄, and H₃PO₄. Insome embodiments, it is desirable to provide a mixture of an organic andinorganic acid. In some embodiments one may use a mixture of acidscomprising those having a pKa ≤3.5 (preferably <2.5, most preferablyless than 1), optionally with minor amounts of other acids havingpKa's>0. It has been found that weaker acids having a pKa of >4, such asacetic acid, do not provide a uniform coatings having the desirableproperties of transmissivity, cleanability, and/or durability. Inparticular, primer coating compositions with weaker acids such as aceticacid typically bead up on the surface of a substrate.

The primer coating composition generally contains sufficient acid toprovide a pH of less than 5, preferably less than 4, most preferablyless than 3. In some embodiments, it has been found that the pH of thecoating composition can be adjusted to pH 5-6 after reducing the pH toless than 5. This allows one to coat pH-sensitive substrates.

Tetraalkoxy coupling agents, particularly tetraalkoxysilanes, such astetraethylorthosilicate (TEOS), and oligomeric forms oftetraalkoxysilane, such as alkyl polysilicates (e.g.,poly(diethoxysiloxane)), may also be useful to improve binding betweensilica nanoparticles. The amount of coupling agent included in thecoating composition should be limited in order to prevent destruction ofthe anti-reflective or anti-fog properties of the coating. The optimalamount of coupling agent is determined experimentally and is dependenton the coupling agent's identity, molecular weight and refractive index.The coupling agent(s), when present, are typically added to thecomposition at levels of 0.1 to 50 percent by weight (wt-%) of thesilica nanoparticle concentration, and more preferably 1 to 15 percentby weight of the silica nanoparticles.

The primed article includes a substrate surface bearing a continuousnetwork of silica nanoparticles agglomerates.

In one embodiment, the particles preferably have an average primaryparticle size of 40 nanometers or less, preferably 20 nanometers orless, and more preferably 10 nanometers or less. The smallernanoparticles, those of 20 nanometers or less, generally provide betterprimer coatings, when acidified, without the need for additives such astetraalkoxysilanes, surfactants or organic solvents. Further, thenanoparticles generally have a surface area greater than 150 m²/gram,preferably greater than 200 m²/gram, and more preferably greater than400 m²/gram. The particles preferably have narrow particle sizedistributions, that is, a polydispersity (i.e., particle sizedistribution) of 2.0 or less, preferably 1.5 or less. If desired, largersilica particles may be added, in amounts that do not deleteriouslydecrease the coatability of the composition on a selected substrate.

In another embodiment, the particles preferable have at least a bimodaldistribution with a silica nanoparticles having average particlediameters of 40 nanometers or less and silica nanoparticles havingaverage particle diameters of greater than 50 nanometers. The silicananoparticles may have average particle diameters up to 500 nanometers.In one embodiment, the bimodal distribution of silica nanoparticles hasa first distribution in a range from 2 nanometers to 15 nanometers and asecond distribution in a range from 20 nanometers to 500 nanometers; afirst distribution in a range from 2 nanometers to 20 nanometers and asecond distribution in a range from 30 nanometers to 500 nanometers oreven a first distribution in a range from 5 nanometers to 15 nanometersand a second distribution in a range from 20 nanometers to 100nanometers. In another aspect, in some embodiments, the weight ratio ofthe first distribution of nanoparticles to the second distribution ofnanoparticles is in a range from 1:99 to 99:1; 10:90 to 90:10; 20:80 to80:20; or even 30:70 to 70:30. In one embodiment, the weight ratio ofthe first distribution of nanoparticles to the second distribution ofnanoparticles is in a range from 1:99 to 99:1.

The nanosilica described in this disclosure may be spherical ornonspherical. The silica nanoparticles are preferably not surfacemodified.

The average particle size may be determined using transmission electronmicroscopy. As used herein, the term “continuous” refers to covering thesurface of the substrate with virtually no discontinuities or gaps inthe areas where the gelled network is applied. The term “network” refersto an aggregation or agglomeration of nanoparticles linked together toform a porous three-dimensional network. The term agglomerates as usedherein refers to linking together (or sintering) of the nanoparticles asshown and described in FIG. 1 of WO 2009/140482. The term “primaryparticle size” refers to the average size of unagglomerated singleparticles of silica.

The term “porous” refers to the presence of voids between the silicananoparticles created when the nanoparticles form a continuous coating.For single layer primer coatings, it is known that in order to maximizelight transmission in air through an optically transparent substrate,and minimize reflection by the substrate, the refractive index of thecoating should equal as closely as possible the square root of therefractive index of the substrate, and the thickness of the coatingshould be approximately one-fourth (¼) of the optical wavelength of theincident light. The voids in the coating provide a multiplicity ofsubwavelength interstices between the silica nanoparticles where theindex of refraction (RI) abruptly changes from that of air (RI=1) tothat of the metal oxide particles (e.g., for silica RI=1.44). Byadjusting the porosity, a primer coating having a calculated index ofrefraction (as shown in U.S. Pat. No. 4,816,333 (Lange, et al.)) veryclose to the square root of the refractive index of the substrate can becreated. By utilizing primer coatings having optimal indices ofrefraction at coating thicknesses equal to approximately one-fourth theoptical wavelength of the incident light, the percent transmission oflight through the coated substrate is maximized and reflection isminimized.

Preferably, the network has a porosity of 25 to 45 volume percent, morepreferably 30 to 40 volume percent, when dried. In some embodiments theporosity may be higher. Porosity may be calculated from the refractiveindex of the coating according to published procedures such as in W. L.Bragg, A. B. Pippard, Acta Crystallographica, volume 6, page 865 (1953).With silica nanoparticles, this porosity provides a coating having anindex of refraction of 1.2 to 1.4, preferably 1.25 to 1.36, which isapproximately equal to the square root of the refractive indices ofpolyester, polycarbonate, and poly(methyl methacrylate) substrates. Forexample, a porous silica nanoparticle primer coating having a refractiveindex of 1.25 to 1.36 is capable of providing a highly anti-reflectivesurface when coated on a polyethylene terephthalate substrate (RI=1.64)at a thickness of 1000-2000 Å. Primer coating layer thicknesses may behigher, e.g., as high as a few microns or mils thick, depending on theapplication, such as for easy-clean of removal of undesiredparticulates, rather than antireflection. The mechanical properties maybe expected to be improved when the coating thickness is increased.

In order to uniformly coat a primer composition onto a hydrophobicsubstrate from an aqueous system it may be desirable to increase thesurface energy of the substrate and/or reduce the surface tension of thecoating composition. The surface energy may be increased by oxidizingthe substrate surface prior to coating using corona discharge or flametreatment methods. These methods may also improve adhesion of thecoating to the substrate. Other methods capable of increasing thesurface energy of the article include the use of primers such as thincoatings of polyvinylidene chloride (PVDC). Alternatively, the surfacetension of the coating composition may be decreased by addition of loweralcohols (C₁ to C₈). In some instances, however, in order to improve thecoating hydrophilicity for desired properties and to ensure uniformcoating of the article from an aqueous or hydroalcoholic solution, itmay be beneficial to add a wetting agent, which is typically asurfactant, to the primer composition.

The term “surfactant” as used herein describes molecules comprisinghydrophilic (polar) and hydrophobic (non-polar) regions on the samemolecule which are capable of reducing the surface tension of thecoating solution. Useful surfactants may include those disclosed in U.S.Pat. No. 6,040,053 (Scholz et al.).

For typical concentrations of silica nanoparticles (e.g., 0.2 to 15percent by weight relative to the total coating composition) mostsurfactants comprise less than 0.1 percent by weight of the coatingcomposition, preferably 0.003 to 0.05 percent by weight, in order topreserve the anti-reflective properties of the coating. It should benoted that with some surfactants a spotty coating is attained atconcentrations in excess of what is needed to achieve the anti-fogproperty.

Anionic surfactants in the primer coating composition are preferred whenadded to improve the uniformity of the resulting coatings. Usefulanionic surfactants include, but are not limited to, those withmolecular structures comprising (1) at least one hydrophobic moiety,such as C₆-C₂₀ alkyl, alkylaryl, and/or alkenyl groups, (2) at least oneanionic group, such as sulfate, sulfonate, phosphate, polyoxyethylenesulfate, polyoxyethylene sulfonate, polyoxyethylene phosphate, and thelike, and/or (3) the salts of such anionic groups, wherein said saltsinclude alkali metal salts, ammonium salts, tertiary amino salts, andthe like. Representative commercial examples of useful anionicsurfactants include sodium lauryl sulfate, available under the tradename TEXAPON L-100 from Henkel Inc., Wilmington, Del., or under thetrade name POLYSTEP B-3 from Stepan Chemical Co, Northfield, Ill.;sodium lauryl ether sulfate, available under the trade name POLYSTEPB-12 from Stepan Chemical Co., Northfield, Ill.; ammonium laurylsulfate, available under the trade name STANDAPOL A from Henkel Inc.,Wilmington, Del.; and sodium dodecyl benzene sulfonate, available underthe trade name SIPONATE DS-10 from Rhone-Poulenc, Inc., Cranberry, N.J.

Where the primer coating composition does not include a surfactant orwhen improved coating uniformity is desirable, it may be beneficial toadd another wetting agent, including those that do not impart durableanti-fog properties, in order to ensure uniform coating of the articlefrom an aqueous or hydroalcoholic solution. Examples of useful wettingagents include polyethoxylated alkyl alcohols (e.g. “Brij™ 30,” and“Brij™ 35,” commercially available from ICI Americas, Inc., and“Tergitol™ TMN-6™ Specialty Surfactant,” commercially available fromUnion Carbide Chemical and Plastics Co., polyethoxylated alkylphenols(e.g., “Triton™ X-100” from Union Carbide Chemical and Plastics Co.,“Iconol™ NP-70” from BASF Corp.) and polyethylene glycol/polypropyleneglycol block copolymer (commercially available as “Tetronic™ 1502 BlockCopolymer Surfactant,” “Tetronic™ 908 Block Copolymer Surfactant” and“Pluronic™ F38 Block Copolymer Surfactant,” all from BASF, Corp.). Ofcourse, any added wetting agent must be included at a level which willnot destroy the anti-reflective or anti-fog properties of the coating,if such features are desired. Generally the wetting agent is used inamounts of less than 0.1 percent by weight of the coating composition,preferably 0.003 to 0.05 percent by weight of the coating compositiondepending on the amount of silica nanoparticles. Rinsing or steeping thecoated article in water may be desirable to remove excess surfactant orwetting agent.

Primer coating compositions are preferably coated on the article usingconventional techniques, such as bar, roll, curtain, rotogravure, spray,or dip coating techniques. The preferred methods include bar and rollcoating, or air knife coating to adjust thickness. In order to ensureuniform coating and wetting of the film, it may be desirable to oxidizethe substrate surface prior to coating using corona discharge or flametreatment methods. Other methods capable of increasing the surfaceenergy of the article include the use of primers such as polyvinylidenechloride (PVDC).

The primer coatings of the present disclosure are preferably applied inuniform average thicknesses varying by less than 200 Å, and morepreferably by less than 100 Å, in order to avoid visible interferencecolor variations in the coating. The optimal average dry coatingthickness is dependent upon the particular primer coating composition,but in general the average thickness of the coating is 100 Å to 10,000Å, preferably 500 to 2500 Å, more preferably 750 to 2000 Å, and evenmore preferably 1000 to 1500 Å, as measured using an ellipsometer suchas a Gaertner Scientific Corp Model No. L115C. Above and below thisrange, the anti-reflective properties of the coating may besignificantly diminished. It should be noted, however, that while theaverage coating thickness is preferably uniform, the actual coatingthickness can vary considerably from one particular point on the coatingto another. Such variation in thickness, when correlated over a visiblydistinct region, may actually be beneficial by contributing to the broadband anti-reflective properties of the coating.

Primer coatings of the present disclosure can be coated on both sides ofa substrate if desired. Alternatively, the coatings of the presentdisclosure may be coated on one side of the substrate.

Once coated, the primed article is typically dried at temperatures of20° C. to 150° C. in a recirculating oven. An inert gas may becirculated. The temperature may be increased further to speed the dryingprocess, but care must be exercised to avoid damage to the substrate.For inorganic substrates, the cure temperature can be above 200° C.After the primer coating composition is applied to the substrate anddried, the coating comprises preferably from 60 to 95 percent by weight(more preferably from 70 to 92 percent by weight) of silicananoparticles (typically agglomerated), from 0.1 to 20 percent by weight(more preferably from 10 to 25 percent by weight) tetraalkoxysilanes andoptionally 0 to 5 percent by weight (more preferably from 0.5 to 2percent by weight) surfactant, and optionally up to 5 percent by weight(preferably 0.1 to 2 percent by weight) wetting agent.

When the primer coating compositions of the disclosure are applied tosubstrates to provide anti-reflection properties, glare is reduced byincreasing the light transmission of the coated substrate. Preferably,the primed substrate exhibits an increase in transmission of normalincident light of at least 3 percentage points and up to as much as 10percentage points or more, when compared to an uncoated substrate, at550 nm (e.g., the wavelength at which the human eye displays peakphoto-optic response). The percent transmission is dependent upon theangle of incidence and the wavelength of light and is determined usingASTM test method D1003-92, entitled “Haze and Luminous Transmittance ofTransparent Plastics.” Preferably, the coated substrates display anincrease in percent transmission of greater than 3 percent, morepreferably greater than 5 percent, and most preferably greater than 8percent when compared with an uncoated substrate, using 550 nm light.When the desired usage involves significant “off-axis” (i.e. non-normal)viewing or unwanted reflections, gains in visibility may be greaterespecially where the reflections approach or exceed in brightness theobject in view.

When antireflection coating is not required, the primer coatingthickness can be 1 to 10 microns.

In some embodiments the primer coating composition itself provides atough, abrasion resistant layer that protects the substrate and theunderlying graphic display from damage from causes such as scratches,abrasion and solvents.

In many embodiments, the primer coating compositions of the presentdisclosure are shelf stable, e.g., they do not gel, opacify, orotherwise deteriorate significantly. Further, in many embodiments, theprimed articles are durable and abrasion resistant.

Coated Articles

In some embodiments, articles of the disclosure comprise a substrate,preferably having a primed surface, which may be of virtually anyconstruction, transparent to opaque, polymeric, glass, ceramic, ormetal, having a flat, curved, or complex shape, and preferably havingformed thereon a continuous network of agglomerated silicananoparticles.

Preferred primer and sulfonate-functional coating compositions of thepresent disclosure provide hydrophilicity to a substrate. They are alsoboth useful in imparting anti-fog properties to substrates coatedtherewith. And, for certain embodiments, they both can impartanti-reflection to substrates coated therewith.

The polymeric substrates may comprise polymeric sheet, film, or moldedmaterial. In some embodiments, where increased transmissivity isdesired, the substrate is transparent. The term transparent meanstransmitting at least 85% of incident light in the visible spectrum(400-700 nm wavelength). Transparent substrates may be colored orcolorless.

In other embodiments, where increased hydrophilicity is desired, thesubstrate may be initially hydrophobic. The compositions may be appliedto a wide variety of substrates by a variety of coating methods. As usedherein, “hydrophilic” is used to refer to a surface that it is wet byaqueous solutions, and does not express whether or not the layer absorbsaqueous solutions. Surfaces on which drops of water or aqueous solutionsexhibit a static water contact angle of less than 50° are referred to as“hydrophilic.” Hydrophobic substrates have a water contact angle of 50°or greater.

Substrates to which the coating compositions of the disclosure can beapplied are preferably transparent or translucent to visible light.Preferred substrates are made of polyester (e.g., polyethyleneterephthalate, polybutyleneterephthalate), polycarbonate,allyldiglycolcarbonate, polyacrylates, such as polymethylmethacrylate,polystyrene, polysulfone, polyethersulfone, homo-epoxy polymers, epoxyaddition polymers with polydiamines, polydithiols, polyethylenecopolymers, fluorinated surfaces, cellulose esters such as acetate andbutyrate, glass, ceramic, organic and inorganic composite surfaces andthe like, including blends and laminates thereof.

In other embodiments, the substrate need not be transparent. It has beenfound that the composition provides easily cleanable surfaces tosubstrates such as flexible films used in graphics and signage. Flexiblefilms may be made from polyesters such as PET or polyolefins such as PP(polypropylene), PE (polyethylene) and PVC (polyvinyl chloride) areparticularly preferred. The substrate can be formed into a film usingconventional filmmaking techniques such as extrusion of the substrateresin into a film and optional uniaxial or biaxial orientation of theextruded film. The substrate can be treated to improve adhesion betweenthe substrate and the primer coating, using, e.g., chemical treatment,corona treatment such as air or nitrogen corona, plasma, flame, oractinic radiation. If desired, an optional tie layer can also be appliedbetween the substrate and the primer coating composition to increase theinterlayer adhesion. The other side of the substrate may also be treatedusing the above-described treatments to improve adhesion between thesubstrate and an adhesive. The substrate may be provided with graphics,such as words or symbols as known in the art.

In still other embodiments, the substrate can be a metal or have a metalsurface (e.g., vapor deposited metals) such as aluminum or stainlesssteel.

Typically the substrate is in the form of a film, sheet, panel or paneof material and may be a part of an article such as a computer case, acell phone case, a computer screen, a cell phone screen, ophthalmiclenses, architectural glazings, decorative glass frames, motor vehiclewindows and windshields, and protective eye wear, such as surgical masksand face shields. The coatings may, optionally if desired, cover only aportion of the article, e.g., only the section immediately adjacent theeyes in a face shield may be coated. The substrate may be flat, curvedor shaped. The article to be coated may be produced by blowing, casting,extrusion, or injection molding.

Articles such as disposable surgical face masks and face shields whichare coated with the anti-reflective, anti-fog compositions of thisdisclosure are preferably stored in single use packages which reduceenvironmental exposure and contamination which can result in decreasedanti-fog properties. Reusable articles are preferably used incombination with a package that protects or completely seals the productfrom environmental exposure when not in use. The material used to formthe packages should be comprised of a non-contaminating material. It hasbeen found that certain materials can result in partial or totalelimination of the anti-fog properties. While not being bound by anytheory, it is currently believed that materials which containplasticizers, catalysts, and other low molecular weight materials whichcan volatilize on aging are sorbed into the coating and result in adecrease in the anti-fog property.

Accordingly, the disclosure provides protective eyewear, such assurgical masks and face shields, as well as ophthalmic lenses, windowsand windshields which have anti-reflective and anti-fog properties.Furthermore, cell phone and computer components are provided which havewipe-away fingerprint surfaces.

Ideally, the sulfonate-functional coating provides easy removal offingerprints (i.e., wipe-away fingerprint surfaces). Significantly, forcertain embodiments, a simple application of gentle wiping is all thatis needed to remove substantially all of the skin oils deposited as afingerprint; however, for preferred embodiments water (e.g., tap waterat ambient temperature) and/or water vapor (e.g., an individual'sbreath) and wiping (e.g., up to a few gentle strokes with a tissue,paper towel, cloth) is all that is necessary to remove substantially allof the skin oils deposited as a fingerprint.

EXAMPLES

Objects and advantages of various embodiments of this invention arefurther illustrated by the following examples, but the particularmaterials and amounts thereof recited in these examples, as well asother conditions and details, should not be construed to unduly limitthis invention. These examples are merely for illustrative purposes onlyand are not meant to be limiting on the scope of the appended claims.

All parts, percentages, ratios, etc. in the examples and the rest of thespecification are by weight, unless noted otherwise. Solvents and otherreagents used were obtained from Aldrich Chemical Company, Milwaukee,Wis. unless otherwise noted.

Materials

-   Polycarbonate (PC) substrates were prepared from “Lexan™ 101”    available from Sabic Innovative Plastics, Pittsfield, Mass.-   Polyethylene terephthalate (PET) substrates were prepared from    “Scothpar™” available from 3M Company, St. Paul, Minn. and flashlamp    treated using conventional methods.-   Aluminum (Al) substrates were prepared from 18 gauge aluminum 5052    available from McMaster-Carr of Robbinsville, N.J.-   Stainless steel (SS) substrates were prepared from 26 gauge 304    stainless steel available from McMaster-Carr of Robbinsville, N.J.-   Float glass plates were obtained from Cardinal Glass of Eden    Prairie, Minn. Artificial sebum was obtained from WFK-Testgewebe    GmbH, Germany.-   “Polystep™ A-18” (linear sodium alpha olefin sulfonate) was obtained    from Stepan Company, Northfield, Ill.-   “Biosoft™ D-40” (linear sodium alkylbenzene sulfonate) was obtained    from Stepan Company, Northfield, Ill.-   NALCO 8691 is 13.3% solids (nominally 13 percent solids) aqueous    colloidal spherical silica dispersion, available as NALCO 8691 from    NALCO Chemical Company, Naperville, Ill.-   NALCO 2326 is 16.2% solids (nominally 16 percent solids) aqueous    colloidal spherical silica dispersion, available as NALCO 2326 from    NALCO Chemical Company, Naperville, Ill.-   Nissan Snowtex ST-OUP is 15.8% solids (nominally 16 percent solids)    aqueous colloidal nonspherical silica dispersion, available as    Snowtex ST-OUP from Nissan Chemical Company, Houston, Tex.-   NPS1: A 2.5 wt-% solution of [Nalco 8691: Polystep A-18 (99:1 w/w)]    in water and was acidified with 1.5 M HNO₃ to pH=2.-   NPS2: A 5 wt-% solution of [Nalco 8691: Polystep A-18 (99:1 w/w)] in    water and was acidified with 1.5 M HNO₃ to pH=2.-   NPS3: A 2 wt-% solution of [Nalco 2326: Nissan ST-OUP: Biosoft™ D-40    (59.6:39.4:1 w/w)] in water and was acidified with 1.5 M HNO₃ to    pH=3.-   Methanol was obtained from VWR International, West Chester, Pa.-   Tetrahydrofuran (THF) was obtained from VWR International, West    Chester, Pa.-   Diethyl ether was obtained from VWR International, West Chester, Pa.-   Dichloromethane was obtained from VWR International, West Chester,    Pa.-   1,3-Propane sultone was obtained from Aldrich Chemical, St. Louis,    Mo.-   1,4-butane sultone was obtained from Aldrich Chemical, St. Louis,    Mo.-   3-(N,N-dimethylaminopropyl)trimethoxysilane was obtained from    Gelest, Morrisville, Pa.-   2-(4-Pyridylethyl)triethoxysilane was obtained from Gelest,    Morrisville, Pa.-   3-Hydroxy-1-propanesulfonic acid sodium salt was obtained from    Aldrich Chemical, St. Louis, Mo.-   3-(N,N-diethylaminopropyl)trimethoxysilanewas obtained from Gelest,    Morrisville, Pa.-   7-Bromoheptyltrimethoxysilane was obtained from Gelest, Morrisville,    Pa.-   Dimethylamine (2M in Methanol) was obtained from Alfa Aesar, Ward    Hill, Mass.-   3-(Triethoxysilyl)propylisocyanate was obtained from Aldrich    Chemical, St. Louis, Mo.-   N,N-dimethylethylenediamine was obtained from Aldrich Chemical, St.    Louis, Mo.-   1,3-bis(dimethylamino)-2-propanol was obtained from Aldrich    Chemical, St. Louis, Mo.-   2-(2-Dimethylaminoethoxy)ethanol was obtained from TCI America,    Portland, Oreg.-   Lithisil™ 25 (lithium silicate) was obtained from PQ Corporation,    Valley Forge, Pa.-   Unless otherwise noted, all parts, percentages, ratios, etc. in the    examples and the rest of the specification are by weight.

Preparative Example 1

Preparation of

coating solution

3-(N,N-dimethylaminopropyl)trimethoxysilane (3.0 grams (g), 14.5millimoles (mmol)) was added to a screw-top jar followed by anhydrousTHF (10 g). To the mixture, 1,3-propane sultone (1.8 g, 14.5 mmol) wasadded over 40 minutes. The combined reaction mixture was warmed to 65°C. and mixed for a period of 14 hours. The solvent was removed from thereaction mixture by evaporation and the solid was diluted to 1 wt-% inmethanol.

Preparative Example 2

Preparation of

coating solution

3-(N,N-dimethylaminopropyl)trimethoxysilane (3.0 g, 14.5 mmol) was addedto a screw-top jar followed by DI water (5.0 g). 1,3-Propane sultone(1.8 g, 14.5 mmol) was added to the mixture over a period of 15 minutes.The combined reaction mixture was warmed to 65° C. and mixed for aperiod of 14 hours. The reaction mixture was diluted to 2 wt-% in waterto obtain the final coating solution.

Preparative Example 3

Preparation of

coating solution

3-(N,N-dimethylaminopropyl)trimethoxysilane (49.7 g, 239 mmol) was addedto a screw-top jar followed by deionized (DI) water (82.2 g) and1,4-butane sultone (32.6 g, 239 mmol). The combined reaction mixture waswarmed to 75° C. and mixed for a period of 14 hours. The reactionmixture was diluted to 2 wt-% in water to obtain the final coatingsolution.

Preparative Example 4

Preparation of

coating solution

2-(4-Pyridylethyl)triethoxysilane (2.0 g, 7.0 mmol) was added to ascrew-top jar followed by DI water (5.0 g). 1,3-Propane sultone (0.9 g,7.0 mmol) was added to the mixture over a period of 15 minutes. Thecombined reaction mixture was warmed to 65° C. and mixed for a period of14 hours. The reaction mixture was diluted to 2 wt-% in water to obtainthe final coating solution.

Preparative Example 5

Preparation of

coating solution

3-(N,N-dimethylaminopropyl)trimethoxysilane (5.0 g, 24.1 mmol) was addedto a screw-top jar followed by DI water (9.7 g) followed by3-hydroxy-1-propanesulfonic acid sodium salt (4.7 g, 24.1 mmol). Thecombined reaction mixture was warmed to 65° C. and mixed for a period of14 hours. The reaction mixture was diluted to 2 wt-% in water to obtainthe final coating solution.

Preparative Example 6

Preparation of

coating solution

3-(N,N-diethylaminopropyl)trimethoxysilane (3.0 g, 14.5 mmol) was addedto a screw-top jar followed by anhydrous THF (10 g). To the mixture,1,3-propane sultone (1.8 g, 14.5 mmol) was added over 15 minutes. Thecombined reaction mixture was warmed to 65° C. and mixed for a period of14 hours. The solvent was removed from the reaction mixture byevaporation and the solid was diluted to 1 wt-% in methanol. When waterwas used as a solvent instead of THF, the fingerprint cleaningperformance was reduced.

Preparative Example 7

Preparation of

coating solution

7-Bromoheptyltrimethoxysilane (5.0 g, 16.7 mmol) was added to ascrew-top vial along with dimethylamine (2.0 M in methanol, 20 milliters(mL)) and heated to 75° C. for a period of 14 hours. After concentrationof the reaction mixture by evaporation, diethyl ether was added and themixture was filtered and concentrated to yield7-(N,N-dimethylaminopropyl)trimethoxysilane. A screw-top vial wascharged with 7-(N,N-dimethylaminopropyl)trimethoxysilane (1.0 g, 3.8mmol) and anhydrous THF (3.0 g). To the reaction vessel, 1,3-propanesultone (0.5 g, 3.8 mmol) was added over a period 10 minutes. Thecombined reaction mixture was heated to 75° C. for a period of 7.5hours. The solvent was removed from the reaction mixture and the solidwas diluted to 1 wt-% in methanol. When water was used as a solventinstead of THF the fingerprint cleaning performance was reduced.

Preparative Example 8

Preparation of

coating solution

A screw-top vial was charged with N,N-dimethylethylenediamine (0.85 g,9.6 mmol) and anhydrous THF (9 mL). To the reaction vessel3-(triethoxysilyl) propylisocyanate (2.60 g, 10.6 mmol) was added over aperiod of 5 minutes. After the reaction was mixed at room temperaturefor 2 hours, 1,3-propane sultone (1.30 g, 10.6 mmol) was added. Thereaction was allowed to mix at room temperature for 12 hours before thesolid was filtered from the mixture and dried. The solid was dissolved(1%) in warm methanol for coating.

Preparative Example 9

Preparation of

coating solution

A screw-top vial was charged with 2-(2-dimethylaminoethoxy)ethanol (1.3g, 9.6 mmol) and 3-(triethoxysilyl)propylisocyanate (2.50 g, 10.1 mmol),and subsequently warmed to 60° C. for 14 hours. The reaction mixture wascooled to room temperature before addition of THF (5 mL) and 1,3-propanesultone (1.30 g, 10.6 mmol). The reaction was allowed to mix at 60° C.for 8 hours before the solid was filtered from the mixture and dried.The solid was dissolved (1%) in warm methanol for coating.

Preparative Example 10

Preparation of

coating solution

A screw-top vial was charged with 1,3-bis(dimethylamino)-2-propanol (1.4g, 9.6 mmol) and 3-(triethoxysilyl)propylisocyanate (2.50 g, 10.1 mmol),and subsequently warmed to 60° C. for 14 hours. The reaction mixture wascooled to room temperature before addition of dichloromethane (5 mL) and1,3-propane sultone (2.80 g, 23.0 mmol). The reaction was allowed to mixat 60° C. for 8 hours before the solid was filtered from the mixture anddried. The solid was dissolved (2%) in water for coating.

Preparative Example 11

Preparation of

coating solution

Preparative Example 11 was prepared as described in U.S. Pat. No.4,338,377 and diluted to 2 wt-%.

Preparative Example 12

Preparation of

coating solution

Preparative Example 12 was prepared as described in U.S. Pat. No.4,338,377 and diluted to 2 wt-%.

Preparative Example 13

Preparative Example 13 coating solution was prepared by neutralizing a2% solution of Preparative Example 11 with NaOH (1.0 M) to pH=7.

Preparative Example 14

Preparative Example 14 coating solution was prepared as a 2.5 wt-%solution of [Lithisil™ 25 lithium silicate: compound of PreparatoryExample 3 (50:50 w/w)] in water.

Preparative Example 15

Preparative Example 15 coating solution was prepared as a 2.5 wt-%solution of [Lithisil™ 25 lithium silicate: compound of PreparatoryExample 11 (50:50 w/w)] in water.

Preparative Example 16

Preparative Example 16 coating solution was prepared as a 2.5 wt-%solution of [Lithisil™ 25 lithium silicate: compound of PreparatoryExample 12 (50:50 w/w)] in water.

Preparative Example 17

Preparative Example 17 coating solution was prepared as a 20 wt-%solution of [Lithisil™ 25 lithium silicate: compound of PreparatoryExample 3 (50:50 w/w)] in water.

Example 1

For Example 1 a series of 7.6 cm×12.7 cm glass plates were coated withcoating solutions prepared as described in Preparatory Examples 1-12using a Kimwipe™ paper tissue (obtained from Kimberly Clark, Roswell,Ga.). Before coating, the glass plates were cleaned using Alconox™detergent (obtained from Alconox, Inc., White Plains, N.J.). The coatedglass plates (i.e., samples) were dried at room temperature and heatedfor 20 minutes at 150° C. After cooling the samples to room temperature,they were rinsed with DI water (600 mL/minute) for 30 seconds. Thesamples were dried with a stream of compressed air. An artificialfingerprint was applied to the coated surfaces using artificial sebumand allowed to stand for a period of time greater than 10 minutes atroom temperature. The ease of removing the fingerprint from the coatedsurfaces was tested using a Taber liner abrader (obtained from TaberIndustries, North Tonawanda, N.Y.) fitted with a 2.5 cm button coveredwith a Kimberly-Clark™ L-30 Wypall™ towel (obtained from Kimberly Clark,Roswell, Ga.) and an applied total load of 350 g. To initiate thefingerprint removal test, each sample was submitted to a 4 second exhaleto generate moisture on the surface of the sample. Upon completion ofthe exhalation the abrader was simultaneously initiated and allowed towipe over the fingerprint for 1 cycle (1 cycle consists of a forwardwipe followed by a backward wipe). After the test was completed a freshtowel was attached for wiping the next sample. The sample was thenvisually inspected and rated. A rating of “Pass” means the fingerprintwas mostly removed and a rating of “Fail” means the fingerprint remainedand/or smeared. Table 1 summarizes the fingerprint removal test data forcoatings on glass plates prepared from Preparatory Examples 1-12 coatingsolutions as well as an uncoated glass plate control.

TABLE 1 Coating solution Fingerprint removal rating Preparatory Example1 Pass Preparatory Example 2 Pass Preparatory Example 3 Pass PreparatoryExample 4 Pass Preparatory Example 5 Pass Preparatory Example 6 PassPreparatory Example 7 Pass Preparatory Example 8 Pass PreparatoryExample 9 Pass Preparatory Example 10 Pass Preparatory Example 11 PassPreparatory Example 12 Pass Uncoated glass plate control Fail

Examples 2-3 and Comparative Example A

For Examples 2 and 3 several stainless steel coupons were cleaned withacetone and dried under a stream of nitrogen gas. Then, the coupons weredip coated with silica nanoparticles by immersing them in NPS1 solutionat a rate of 18 millimeters per minute (mm/min), allowing them remain inthe coating solution for 20 seconds, and removing at 18 mm/min rate. Thesamples were dried at room temperature, and then were heated at 150° C.for 10 minutes. The samples were subsequently dipped into coatingsolution of Preparatory Example 3 (for Example 2) or coating solution ofPreparatory Example 11 (for Example 3) in the same manner as that usedfor forming silica nanoparticle coatings. The samples were allowed todry at room temperature before a final heat treatment at 150° C. for 10minutes. For Comparative Example A, the stainless steel coupons werecleaned with acetone and dried under a stream of nitrogen gas but, werenot coated.

Examples 4-5 and Comparative Example B

For Examples 4 and 5, several aluminum coupons were cleaned with acetoneand dried under a stream of nitrogen. Next, the coupons were submergedinto a 4 wt % solution of H₂SO₄ for 30 minutes. The samples were rinsedwith DI water and dried with a stream of nitrogen. Then, the couponswere dip coated with silica nanoparticles by immersing them in NPS1solution at a rate of 18 mm/min, allowing them remain in the coatingsolution for 20 seconds, and removing at 18 mm/min rate. The sampleswere dried at room temperature, and then were heated at 150° C. for 10minutes. The samples were subsequently dipped into coating solution ofPreparatory Example 3 (for Example 4) or coating solution of PreparatoryExample 11 (for Example 5) in the same manner as that used for formingsilica nanoparticle coatings. The samples were allowed to dry at roomtemperature before a final heat treatment at 150° C. for 10 minutes. ForComparative Example B, the aluminum coupons were cleaned with acetoneand dried under a stream of nitrogen gas but, were not further treatedor coated.

Examples 6-7 and Comparative Example C

For Examples 6 and 7, several PET films were coated with silicananoparticles by using NPS1 solution and a Meyer rod (#6), and allowingthe coated films dry at room temperature before heat treating for 15minutes at 150° C. The samples were subsequently coated with coatingsolution of Preparatory Example 3 (for Example 6) or coating solution ofPreparatory Example 11 (for Example 7) in the same manner as that usedfor forming silica nanoparticle coatings. The coated films were dried atroom temperature before a final heat treatment of 150° C. for 10minutes. For Comparative Example C, the PET films were not coated.

Examples 8-9 and Comparative Example D

For Examples 8 and 9, several PC plates were coated with silicananoparticles by using NPS2 solution and a Meyer rod (#6), and allowingthe coated films dry at room temperature before heat treating for 15minutes at 150° C. The samples were subsequently coated with coatingsolution of Preparatory Example 3 (for Example 8) or coating solution ofPreparatory Example 13 (for Example 9) in the same manner as that usedfor forming silica nanoparticle coatings. The coated PC plates weredried at room temperature before a final heat treatment of 150° C. for10 minutes. For Comparative Example C, the PC plates were not coated.

The samples from Examples 2-9 and Comparative Examples A-D were testedfor their cleanability (of fingerprints) as well as the durability ofthe coatings for maintaining their easy cleanability (of fingerprints).For the test, a facial oil fingerprint was applied to the coatedsurfaces of samples from Examples 2-9 and Comparative Examples A-D usingfacial oil and the samples were allowed to stand for a period of timeless than 5 minutes at room temperature. Then, the samples were wipedwith a facial paper tissue (Surpass' Facial Tissue from Kimberly Clark,Roswell, Ga.) immediately after breathing on the samples. Removal of thefingerprints was visually examined. If the fingerprint was not removedno further testing was done for that sample. If the fingerprint wasremoved successfully, then those samples were further tested by rinsingthe surface with DI water and visually determining if the water formed acontinuous film (i.e., hydrophilic coating). If the water formed acontinuous film, then the sample was further tested for durability ofthe coatings by using the test method described above in Example 1.After each cycle of the test, a facial oil fingerprint was reapplied onthe sample and the test was repeated. Total number of cycles that thefingerprint was successfully removed was determined for each of Examples2-9 samples and reported below in Table 2. For Comparative Examples A-Dthe number of cycles was zero since the fingerprints were not easy toremove from them.

TABLE 2 Example Durability (cycles) 2 >20 3 >20 Comparative A 0 4 >205 >20 Comparative B 0 6 >20 7 >20 Comparative C 0 8 >20 9 >20Comparative D 0

Examples 10-12 and Comparative E

For Examples 10-12, several PET films were coated with silicananoparticles by using NPS3 solution and a Meyer rod (#6), and allowingthe coated films dry at room temperature before heat treating for 15minutes at 150° C. The samples were subsequently coated with coatingsolution of Preparatory Example 14 (for Example 10), coating solution ofPreparatory Example 15 (for Example 11) or coating solution ofPreparatory Example 16 (for Example 12) in the same manner as that usedfor forming silica nanoparticle coatings. The coated PET films weredried at room temperature before a final heat treatment of 150° C. for10 minutes. For Comparative Example E, the PET films were not coated.

The samples from Examples 10-12 were tested for their cleanability (offingerprints). For the test, a facial oil fingerprint was applied to thecoated surfaces of samples from Examples 10-12 using facial oil and thesamples were allowed to stand for a period of time less than 5 minutesat room temperature. Then, the samples were wiped with a facial papertissue (Surpass™ Facial Tissue from Kimberly Clark, Roswell, Ga.)immediately after breathing on the samples. Removal of the fingerprintswas visually examined. If the fingerprint was removed successfully, thenthose samples were further tested by rinsing the surface with DI waterand visually determining if the water formed a continuous film (i.e.,hydrophilic coating). A rating of “Pass” means the fingerprint wasmostly removed and a rating of “Fail” means the fingerprint remainedand/or smeared.

TABLE 3 Example Fingerprint removal rating 10 Pass 11 Pass 12 PassComparative E Fail

Example 13

For Example 13 a series of stainless steel plates were coated withcoating solution prepared as described in Preparatory Examples 17 usinga Kimwipe™ paper tissue (obtained from Kimberly Clark, Roswell, Ga.).Before coating, the stainless steel plates were cleaned using Alconox′detergent (obtained from Alconox, Inc., White Plains, N.J.). The coatedstainless steel plates (i.e., samples) were dried at room temperatureand heated for 30 minutes at 150° C.

The sample from Example 13 was tested for its cleanability (offingerprints) as well as the durability of the coatings for maintainingtheir easy cleanability (of fingerprints). For the test, a facial oilfingerprint was applied to the coated surface of the sample from Example13 using facial oil and the sample was allowed to stand for a period oftime less than 5 minutes at room temperature. Then, the sample was wipedwith a facial paper tissue (Surpass™ Facial Tissue from Kimberly Clark,Roswell, Ga.) immediately after breathing on the samples. Removal of thefingerprints was visually examined. If the fingerprint was not removedno further testing was done for that sample. If the fingerprint wasremoved successfully, then the sample was further tested by rinsing thesurface with DI water and visually determining if the water formed acontinuous film (i.e., hydrophilic coating). If the water formed acontinuous film, then the sample was further tested for durability ofthe coatings by using the test method described above in Example 1.After each cycle of the test, a facial oil fingerprint was reapplied onthe sample and the test was repeated. For Example 13 samples, thefingerprint was successfully removed for more than 20 cycles.

The complete disclosures of the patents, patent documents, andpublications cited herein are incorporated by reference in theirentirety as if each were individually incorporated. Variousmodifications and alterations to this invention will become apparent tothose skilled in the art without departing from the scope and spirit ofthis invention. It should be understood that this invention is notintended to be unduly limited by the illustrative embodiments andexamples set forth herein and that such examples and embodiments arepresented by way of example only with the scope of the inventionintended to be limited only by the claims set forth herein as follows.

What is claimed is:
 1. A coating composition comprising: a zwitterioniccompound comprising sulfonate-functional groups and (a) alkoxysilanegroups and/or (b) silanol-functional groups; alcohol and/or water; and atetraalkoxysilane, oligomers thereof, lithium silicate, sodium silicate,potassium silicate, silica, or combinations thereof.
 2. The coatingcomposition of claim 1, wherein the coating composition comprises nogreater than 20 wt % of the zwitterionic compound.
 3. The coatingcomposition of claim 1, wherein the coating composition comprises 0.1 to20 wt % of the tetraalkoxysilane, oligomers thereof, lithium silicate,sodium silicate, potassium silicate, silica, or combinations thereof. 4.The coating composition of claim 1, wherein the zwitterionic compound is


5. A coated article comprising a substrate surface, a primer coatingdisposed on the substrate surface, and a sulfonate-functional coatingbonded to the primer coating through siloxane bonds, wherein thesulfonate-functional coating is derived from the coating composition ofclaim 1 and wherein the primer coating provides —OH groups on thesurface of the substrate.
 6. A coated article comprising a substratesurface, a nanoparticle-containing primer disposed on the substratesurface, and a sulfonate-functional zwitterionic coating bonded to thenanoparticle-containing primer through siloxane bonds, wherein thenanoparticle-containing primer comprises agglomerates of silicananoparticles having average particle diameters of 40 nanometers orless, said agglomerates comprising a three-dimensional porous network ofsilica nanoparticles, and the silica nanoparticles are bonded toadjacent silica nanoparticles wherein the sulfonate-functional coatingis derived from the coating composition of claim
 1. 7. A method ofcleaning a surface, the method comprising; wiping thesulfonate-functional coating of the coated article claim 6 havingfingerprints on the sulfonate-functional coating; and removing thefingerprints.
 8. The method of claim 7 further comprising applying waterand/or water vapor to the fingerprints and removing the fingerprints bywiping.
 9. A method of treating a substrate surface, the methodcomprising: applying a primer coating composition to the substratesurface to form a primed surface having —OH groups thereon; contactingthe primed surface having —OH groups thereon with the coatingcomposition of claim 1; and drying the coating composition to form asulfonate-functional coating comprising at least a monolayer of thezwitterionic composition bonded to the primer coating through siloxanebonds; wherein fingerprints are removable from the driedsulfonate-functional coating with wiping.
 10. The method of claim 9wherein applying a primer coating composition to the substrate surfacecomprises: contacting the substrate surface with ananoparticle-containing coating composition, wherein thenanoparticle-containing coating composition comprises: an aqueousdispersion having a pH of less than 5 comprising silica nanoparticleshaving average particle diameters of 40 nanometers or less, and an acidhaving a pKa of ≤3.5; and drying the nanoparticle-containing coatingcomposition to provide a silica nanoparticle primer coating on thesubstrate surface.
 11. The method of claim 10 wherein the silicananoparticles have average particle diameters of 20 nanometers or less.12. The method of claim 9 wherein fingerprints are removable from thedried sulfonate-functional coating with water and/or water vapor andwiping.
 13. A method of treating a substrate comprising a metal ororganic polymeric surface to improve fingerprint removal, the methodcomprising: contacting the metal or organic polymeric surface with thecoating composition of claim 1; and drying the coating composition toform a sulfonate-functional coating comprising at least a monolayer ofthe zwitterionic compound bonded to the substrate surface throughsiloxane bonds; wherein fingerprints are removable from the driedsulfonate-functional coating with wiping.
 14. The coating composition ofclaim 1, wherein the coating composition comprises lithium silicate,sodium silicate, potassium silicate, or combinations thereof.
 15. Thecoating composition of claim 1, wherein the coating compositioncomprises a tetraalkoxysilane.
 16. The coating composition of claim 1,wherein the coating composition comprises an alkyl polysilicate.
 17. Thecoating composition of claim 1, wherein the composition is free of acatalyst.